If the U.S. Supreme Court had wanted to make history, it could have: Striking down the individual mandate in the health-care law would have been the most weighty Supreme Court ruling since Franklin Roosevelt’s first New Deal was ruled unconstitutional three-quarters of a century ago.

By upholding the individual mandate -- after honestly acknowledging that making people buy insurance is a tax -- the court chose the more cautious course.

In the spirit of Justices Oliver Wendell Holmes and Felix Frankfurter, the court adopted the strategy of judicial restraint. The man most responsible for this comes as a surprise: Chief Justice John Roberts, a tried and tested conservative appointed by George W. Bush to the near-universal plaudits of the right. Roberts said in his confirmation hearings that he believed in judicial restraint. That has become a cliche, repeated by every would-be judge raising a right hand before a Senate committee. When the chips were down, Roberts did exactly what he had sworn to do under oath. He stayed the court’s hand and rejected activism.

The court’s explanations were sufficiently complex that CNN briefly reported the mandate had been struck down. But the core logic of the holding was a model of analytic clarity. To require people to buy insurance or else pay a penalty is a tax. The Constitution gives Congress the power to tax in order to accomplish its legitimate goals. Calling the mandate what it in fact is makes this result crystal-clear.

Word Choice These words sent a direct message to Democratic politicians who refused to call the mandate a tax: You should have told us the truth in the first place. Had the mandate been called a tax from the beginning, all this legal wrangling might never have occurred. It would have been essentially impossible to argue that the mandate was unconstitutional if the bill had directly relied upon the taxing power.

Of course, politicians are unlikely to take this object lesson seriously. Calling the mandate a tax might have stopped it from passing. Now, the mandate has been upheld. The Democrats’ game of bait-and-switch worked -- after a fashion. Now the drama of the last several months, and the serious worry about the court striking down the president’s signature domestic policy achievement, can be conveniently forgotten.

What is most shocking about the outcome is who brought it about: Roberts, not Justice Anthony Kennedy, cast the deciding fifth vote to uphold the law. When Roberts was up for confirmation, many liberal insiders to the world of the Supreme Court bar were optimistic that he would be a reasonable and evenhanded chief: a conservative, of course, but one who played by the rules. He had little written record to go on, so no detail was too small to escape comment. While still a lawyer, Roberts had occasionally participated alongside liberals in the private, informal moot courts that are part of the preparation for a Supreme Court argument. Once he became chief justice, however, Roberts seemed to many liberals to have reverted to his origins as a clerk for former Chief Justice William H. Rehnquist and a longtime supporter of the Federalist Society, a powerful conservative legal organization. His decisions have for the most part been consistent with those of Justices Samuel Alito, Antonin Scalia and Clarence Thomas, the conservative bloc. Together these four conservatives have won when Kennedy joined them and lost when he defected to the liberal side.

Historically Important In the health-care case, Kennedy joined the conservative dissent. This is itself worthy of comment, because Kennedy has become a historically important liberal justice through his opinions on gay rights and on habeas corpus rights for detainees at Guantanamo Bay, Cuba. But Kennedy has remained a conservative on issues of the government’s power to regulate; and in the end, after all the guessing about his views, he stuck with that position here. One can only speculate on what Kennedy might have done had Roberts not given him the option of joining the conservatives in dissent.

Roberts did wave the conservative standard on the question of Congress’s power to regulate commerce, squarely stating that the regulation of inaction would have been too great an extension of the Commerce Clause power. Yet he balked at stopping Congress from imposing a tax. Conservatives who want to make the health-care plan into a central campaign issue can take some small solace in that the court has called the individual mandate a tax. But there will surely be major shock among those who counted on Roberts to toe the party line, as there is shock among those liberals who had given up on the vision of Roberts as a lawyer’s lawyer.

What explains this result? One possibility is that John Roberts, former law clerk, former high-powered Supreme Court litigator and now chief justice, loves the Supreme Court more than he loves political conservatism. A student of the history of the court -- and as a participant in history -- Roberts knew the consequences of striking down the individual mandate: He would have been attacked by the president and the news media as the chief of the most activist conservative court since the 1930s. For “the Roberts Court” to become a title of infamy would have been a sadly negative culmination of a highly successful career.

Then there is that most old-fashioned of motivations: principle. Frankfurter, who did more than anyone to popularize the idea of judicial restraint, was a liberal New Dealer who became a judicial conservative because he stuck with the principle of restraint even when liberals had five votes.

Roberts now enters the pantheon of true judicial conservatives, judges who hold back from activist results no matter how it affects presidential politics. By helping the court avoid making history, Roberts’s place in history is assured.